mixture screw setting

I was working on my 82' XJ650 Maxim's carbs the other day and I started the turn out what I believe to be a pilot mixture screw before realizing that I shouldn't have done so. In the Haynes manual, it pretty clearly states that you shouldn't adjust them, but they don’t mention a setting that they can be reset to if they are changed.

Does anyone know what would be a good guess for the one I backed out? Would it be a good to assume that the PO may have tried to adjust these and just go ahead and reset them all?

By the way, this is the screw that is right next to the choke needle thing on top of the carb...

I also think it's funny that the Haynes manual is very adamant about the fact that it's a "cold start mechanism" and not a "choke"... they have like a whole paragraph about it... Ha!

 

Haynes are correct.

It is not strictly a choke (which closes and restricts the air intake side of the carb usually with an extra butterfly valve) causing more pure fuel to be sucked into the engine.

In this case, the airflow is left alone and the air/fuel ratio is enriched by allowing extra fuel in via fuel enrichment jets, hence the cold starting mechanism.

 

I just did my carbs. PO had them varying from 1 1/4 to 6 1/2. I set them all at 3 1/4 and the bike fired right up. I backed them out to 3 1/2 and the bike seemed to run marginally better.

 

You have 3 others that you can count how many turns until they seat and use this info to set the one you played with. Unless of course they are all different, then I would go with the 3 turns out which seems to be a common figure coming up on other threads.

 

If you are going to set those mixture screws right, you need to use a colortune or an exhaust gas analizer.

But, the norm seems to be out about 3 turns, mine are only out about
1 3/4 turns (due to a carb mod I did)
Been sorry I did it too! My mileage droped but my bike ran better.
I used a 1/16 drill bit to open or relieve the opening on the float bowl cover that the brass pickup tube hangs into in the float bowl cover.

 

In my readings i found out that i should use a sync stick and a color tuner, Right? My next question is, the screw that im turning is the one that is between the carbs? ive read some thing about drilling the brass cap that is no the carb its self.What is the screw for that is under that cap, If there is a screw under it on my bike. Will i have to do that in order to tune them?

 

The screw under the cap is for the pilot screw. It is for the idle mixture. If you search this site on for carb sync you will find all kinds of info. To adjust sync the screws between the carbs are the correct ones. They have to be done in a certain order though.

 

Should the screw under the cap be messed with at all. Since it has that brass cap on it, it makes me feel that Yamaha did not want people touching it. or are my feelings wrong.

 

It was more a matter of keeping the EPA happy, by making it a bit more difficult for the average owner to start fiddling with the idle mixture. Washington dictated tamper-discouraging idle adjustment plugs, and Yamaha had to comply in order to sell bikes here.

The plugs also prevented someone from accidentally adjusting them.

When you service/clean the carbs, removing the idle screws is a necessary part of the task...and the manual clearly shows you how to re-adjust them once you've reassembled the carbs. Messing with them is not verboten, you just need to understand what's going on before you start tweaking things.

Anywhere around 2.5 turns out after gently seating the idle screw will put you in the ballpark. There is no magic fixed setting, just a range of adjustment. More than three turns indicates a restriction in the fuel side of the idle circuit. Less than 1 turn points to the opposite.

The proper idle screw setting is somewhere in between. After the engine is fully warmed up, you can fiddle some more to get it as good/smooth as possible, for the time being.

The only way to really get the idle adjustment right is to do so as the last part of a full tuneup. You need to have the valves in adjustment, and clean carbs with the float levels properly set, or tweaking the idle mixture will just be compensating for something(s) not being quite right.

 

Thanks Bosozoku, that tid bit of info helps me out alot, Im in the waiting stage now that i have ordered my carb stick, and colortune tool,valve cover gasket, shim tool, and in the meen time im making one of thoughs yics tools. And thoughs feelings went away now too.

 

Here's an interesting XJ-FunFact.

A "Special Tuning Factoid"

Just about ... "To the man" ... for all of those who have done a complete Carb Cleaning and Overhaul ... and who have reported their findings and results, in this forum, after adjusting Idle Mixtures with the ColorTune Plug, have reported that their motorcycles ran much better when the Pilot Screws were adjusted further OUT than what is recommended as "Factory Preset"

Factory Preset = 2-1/2 Turns OUT from bottomed-out.

ColorTuned Mixture Settings
(Averaged) = 3 to 3-1/4 Turns OUT ( +/- 1/8 )

Maybe it's three and a quarter. Hey, it could be a little less. For you, you're setting-up ... just to get the bike running a little better; how does three sound?

 

I have a 82 Yamaha 750 Seca and I am having an idle problem. The idle will not come down right away after I tap the throttle. I think I am running rich. How do I adjust this. I dont know where the fuel mixture screw or air mixture screws are. Can someone help? thanks

 

Just reinstalled carbs on my 80 650 Maxim non yics. Did adjust screws starting at 2/1/2 turns from bottom and ended up at about 4 on each. Worked left to right slowly till motor peaked on each and always adjusting idle down to a grand after each carb. Not sure if this will help my cold start problem but it does run much beter warm. THANKS Rick

 

If you can't spot the screws ... (on the top - 12 O'Clock - close to the manifold - probably still hidden under the Factory anti-tamper plug - a little brass plug to the right of the enrichment circuit valve {choke} - you need to get the plugs out)

Good news ... the screws aren't damaged yet.

Don't adjust those screws until you carefully grind the head of a screwdriver to FIT the slot of that screw with ...

NO slack, No side-to-side end-play, zero lash, a perfect fit ... create the tool to fit the slot perfectly.

 

Interesting factoid indeed... when I pulled my carbs apart, one of the things I did was count how many turns out from bottom each one was, before removing them. Every single one of them was exactly two turns out. So, when I put them back in, that's where they went.

Might play into your theory that my machine was running lean, yes?

 

Running lean is real bad news.

I've written why running lean is the worst possible situation for a aluminum air-cooled engine, many, many times before.

If you are running lean, you'd do well to rectify the situation before a calamity ensues.

 

Mines an '82 750 Seca with after market mufflers and Uni foam air filter. I have the stock jets in with the air screws turned out 3 turns on each carb. In the cool weather lately, I only use the choke sparingly to start and let it warm up a little with no choke. It runs smooth on take off and like a cat on fire out on the road. I may eventually get a colortune to see just exactly where I'm at with each carb. I think according to the plugs, it's about as close as it's ever going to be and runs good enough for me. >PD<

 

You are most likely running LEAN, since a rich bike will typically sputter or flood. Reset all of your mixture screws to 3 to 3.5 turns out.

NOTE: this is exactly the situation I had with my bike after cleaning the carbs. My mixture was way lean and my bike would not return to idle after a rev. Richening it up fixed it immediately.

 

I will give that a try, I am assuming I have to take the tank off to do that? Great I have a full tank of gas in the darn thing. Or is there a tool I can get to do this? Thanks!

 

The neatest trick going for a "Tweak-tool" is:

Take a "Pocket-clip" small, CRAFTSMAN screwdriver ... Saw-off the top of the handle ... just above the metal shank.
Cut-off half of the shank.
Grind the end to be a Pilot Screw -- Special Tool.
(Grind the end to fit the screw slot ~> Perfectly - with NO slop or free play.
Mark the 4 "Sides" of the handle with a Visual indicator (of your choosing) to indicate: 0, - 1/4, - 1/2, - 3/4,

You'll have a "Tweaker" ... and by keeping track of where you set the Screws ... you can micro-tweak without pulling the tank!

 

I set my mixture screws and it runs like a top. BUT --- I now see that when the throttle returns it does not go all the way down. If I hold my finger on the throttle screws and put some pressure on them and reve the engine the bike willl return to idle perfectly. But when I dont help it is will not close that extra 16th of an inch to normal idle. Are my throttle springs wore out? Do I have something binding? I dont think the cable is sticky becasue it has slack in it when close all the way.

 

sounds like you just need to turn the mai idle screw counterclock wise just a touch. this should be on the back of the carbs above the starter, between the inner two carbs. it is large and turnable by hand, if your hand fits in there. your all set now, go for a ride.

 

I have an '82 XJ650J - got it with the carbs so gunked up I couldn't even twist the throttle! Took them off, cleaned them, but feared going 'too deep'. Well - no luck getting her started (previous owner said it had sat for 2 years - more likely 3 or 4...).

Off came the carbs again and I went through, using Ric's FAQ to COMPLETELY clean them! Fought with the rubber connectors again.. and she FIRED RIGHT UP! (last night at 8pm!)

Here is the relevance to this thread - all mixture screws had been out 4 to 4 1/2 turns, so I guess that would indicate some restriction in the idle circuit. I set them all to about 3 or so.. and the bike now runs! I'll play a bit more, since I left the sync screws as they were. Next stop - fine tuning...

 

Protect what you have done so-far ... by installing a small, see-thru, inline fuel filter in the supply line going down to the carbs.

Let anything that might spoil your effort get stopped before it causes a problem.

 

First thing I did when I replaced the fuel line a few weeks ago! Prett cheap insurance!

by the way - what is the total length of the custom mixture adjustment tool that you made out of that craftsman pocket screwdriver?

Can't be more than a few inches...

 

I have made a few carb adjustment screwdrivers for myself and friends,I use the screwdriver bits that go into the end of a drill,they have a flat grind instead of the tapered grind on most regular screwdrivers,you just grind diameter down as needed then I tack weld a nut on top to turn,I'm sure if welding isnt a option for you you could soilder or even epoxy a small nut on.I have also used differant color paint or differant # of center punch marks on flats of nut to keep track of screw adjustment..

 

2-7/8th's -- 7.2 cm

RM

 

I made a tool like that.. so heres another question for ya. The diaphrams on top of carbs have 2 sqrews on topi the brass hole your needle valve is atatched to. And i nwed to know if theyre supposed to be out at all?
Im new to carburarors.. please help

 

Nothing in the diaphrams needs to be adjusted, but from your description I'm not sure you are talking about the part that I am.

Please keep all questions about your bike in your thread.
XJ550 Maxim Starter Motor wiring question.

 

My appologize i didnt realize my carburetor questions fit in along with starter wiring questions.. Seems appropriate to me to keep obvious opposite problems in seperate conversations.. correct me if im wrong but in a swrvice manual would you go searching through a chapter labeled starter wiring when your looking to fix a carburator issue??

I would certainly hope not, and if you did i wouldnt want you working on my bike..

 

One thread per bike makes it easy for us to keep track of all the work that has been done. This makes it easier to diagnose symptoms across interrelated systems, and prevents us from asking questions (or providing the same advice) multiple times and in multiple threads (particularly in threads that are over a decade old and about another person's machine) .

History matters.

FWIW the troubleshooting portion of a service manual is all in one section.